1. Field of the Invention
The present invention relates to semiconductor processing and, in particular, concerns a chemical vapor deposition (CVD) technique for forming conductive layers, such as platinum-rhodium layers, in a manner that results in better adhesion of the component layer on the surface of a semiconductor device and better morphology of the layer.
2. Description of the Related Art
Modern semiconductor chemical vapor deposition (CVD) technology has provided fabrication procedures for the development of VLSI (Very-Large-Scale Integration) and ULSI (Ultra-Large-Scale Integration) circuitry. Even though the number of surface mounted semiconductor devices has significantly increased, the surface density is often limited by the finite quantity of real estate on the semiconductor wafer surface. As a result, the finite surface density limitation has induced growth in the vertical direction of modem semiconductor devices. This often requires multiple levels of the conductive interconnects that often, in turn, require numerous metallic-based deposition layers.
As the size of the conductive elements has decreased to accommodate higher density of components, many conventional semiconductor processing techniques for forming conductive elements are forming conductive elements that exhibit more gaps and pinholes and poorer adhesion to the substrate. One particular CVD deposition technique utilized for forming conductive elements is Metal-organic Chemical Vapor Deposition (MOCVD). However, conventional MOCVD techniques alone cannot always compensate for the relatively poor adhesion and morphology that occurs in smaller devices.
For example, complex chemical reactions that occur during the formation of semiconductor devices dictate the final composition of the deposited layer, which may be different than the intended composition. Specifically, the grain structure within the deposited layer may vary depending on the growth rate and the growth environment during the manufacturing and deposition process. A variance in the grain size and grain structure within deposited layers of similar composition and thickness may interfere with or alter the conduction characteristics of electrical current flow through the grain interfaces.
A typical MOCVD technique is as follows. A precursor gas, comprising at least one conductive component or element, and other reactants are introduced into a CVD chamber, and the conductive element carried by the precursor gas is then deposited onto the semiconductor surface of the semiconductor substrate through thermal decomposition. The precursor gas may often be a metal-organic compound, wherein conductive atoms may be bonded to organic compounds, which allows the conductive atoms to be transferred to the semiconductor surface in a gas phase. This enables the conductive atoms, such as platinum and rhodium, to be deposited over the surface of the semiconductor substrate surface as the metal-organic compound facilitates conventional step coverage.
In the prior art, there is generally only a single deposition step such that the precursor gas is introduced into the CVD chamber until enough conductive molecules have been deposited on the exposed semiconductor surface to form a conductive element of a desired thickness. However, as discussed above, conventional MOCVD techniques can result in poor adhesion and poor morphology of the deposited conductive element. This problem is exacerbated in higher density applications requiring smaller conductive components.
From the foregoing, it will be appreciated that there is a need for an improved conductive layer processing technique for depositing, in one embodiment, conductive materials onto a semiconductor substrate surface such that improved substrate adhesion and improved morphology may be obtained without a significant increase in the cost of manufacturing the conductive film layer. To this end, there is also a need for a more efficient method of depositing conductive elements, such as platinum and rhodium, in a manner that exhibits an improved grain interface structure and greater compositional uniformity.